One of many techniques for filtering air is the cyclonic filter. In this technique, air is caused to swirl in a cylindrical enclosure.
An example of a cyclonic filter may be found in Conrad et al., U.S. Pat. No. 6,312,594. Cyclone separators are devices that utilize centrifugal forces and low pressure caused by spinning motion to separate materials of differing density, size and shape. Particles in the air are forced to the outside of the cylinder by inertia (centrifugal force). Due to surface effects, the air flow at the wall is slower. The slow air layer is incapable of suspending many of the particles, so these particles drop to the bottom of the device. The following is a description of the operating principles of a cyclone separator in terms of its application to removing entrained particles from a gas stream, such as may be used in a vacuum cleaner.
The example cyclone separator has an inlet pipe and a main body comprising a cylinder. The particle laden gas stream is injected through inlet pipe, which is positioned tangentially to the interior wall of the cylinder. The shape of the cylinder induces the gas stream to spin creating a vortex. Larger or more dense particles are forced outwards to the walls of the cyclone separator, where the drag of the spinning air as well as the force of gravity causes them to fall down the walls into an outlet or collector. The lighter or less dense particles, as well as the gas medium itself, reverses course near the bottom center of the cylinder and pass upwardly through the low pressure center of the vortex and exit the separator via an outlet that is positioned in the upper portion of the cylinder.
The separation process in cyclones generally requires a steady flow free of fluctuations or short term variations in the flow rate. The inlet and outlets of cyclone separators are typically operated open to the atmosphere so that there is minimal pressure difference between the two. If one of the outlets must be operated at a back pressure, both outlets would typically be kept at approximately the same pressure.
However, as noted above, many of the smaller and/or lighter particles are not precipitated out and additional filters must be used at the outlet of the cyclonic device. These filters require repeated cleaning and may clog permanently, requiring replacement. This invention is directed to a device for minimizing those filters.